XPath is a W3C language standard that can be used to address or query parts of an XML document. It models an XML document as a tree of nodes, which can include element nodes, attribute nodes and/or text nodes. XPath can be used to identify a subset of an XML document by matching, or determining whether a node matches a pattern, similar to how SQL can be used against a database. In the typical case, an expression written in the XPath language is evaluated against an XML document to determine which parts of the document ‘match’ the XPath. In order to do this, the XML document must be parsed and represented in memory. One of the standard representations of XML is the Document Object Model (DOM). DOM model presents an XML document as a hierarchy of nodes through which one can navigate arbitrarily. This approach provides a lot of flexibility, but comes at a cost in terms of efficiency and memory use, as the entire document must be brought into memory at one time.